ICDs Spark Drop in Cardiac Arrests

Action Points

Over the last decades, a gradual decrease in ventricular fibrillation as initial recorded rhythm during resuscitation for out-of-hospital cardiac arrest has been noted. This study from the Netherlands was designed to evaluate the contribution of implantable cardioverter defibrillator therapy to this decline.

Note that the study found that ICD therapy explained a decrease corresponding with 33% of the observed decline in out-of-hospital cardiac arrest associated with ventricular fibrillation.

In one province in the Netherlands, incidence of resuscitation for cardiac arrest due to ventricular fibrillation dropped from 21.1 per 100,000 persons per year to 19.4 over the course of a decade as ICDs became more widespread (P<0.001), Rudolph Koster, MD, PhD, of Academic Medical Center in Amsterdam, and colleagues reported online in Circulation: Journal of the American Heart Association.

The shift could account for about 33% of the decline in out-of-hospital cardiac arrest due to ventricular fibrillation seen in the study, they wrote.

A number of studies have already noted a gradual decrease in the incidence of ventricular fibrillation as the initial rhythm during resuscitation for an out-of-hospital cardiac arrest. There hasn't been a clear explanation for the decline, but many suspect the wider use of ICDs could have something to do with it.

So Koster and colleagues looked at a database of all out-of-hospital cardiac arrest resuscitation attempts in the province of North Holland that occurred from 1995 to 1997 and again from 2005 to 2008.

They noted that the first ICD implementation in the Netherlands was performed in 1984 but it wasn't until reassuring results from large randomized controlled trials published in 1997 that the devices saw wider use. Thus, they collected data on ICD interrogations from all ICD patients in the area and identified all relevant shocks from 2005 to 2008.

They also calculated the number of prevented arrest episodes, considering that only part of the appropriate shocks would result in avoided resuscitation.

The mean age of patients in both time periods was 64 and about 75% were men.

Overall, they found that the incidence of out-of-hospital cardiac arrest with ventricular fibrillation fell by 3.6 per 100,000 person-years during the 10-year period of the study.

Ventricular fibrillation as the presenting rhythm also declined during those two time periods, from 63% to 47% (P<0.001).

During the latter period, 1,972 ICD patients received 977 shocks. Of these shocks, 339 were given to 166 patients for a proven life-threatening arrhythmia.

Koster and colleagues estimated that in this population, 194 instances of life-threatening arrhythmia were successfully aborted by ICD shocks.

Assuming that a life-threatening arrhythmia would have led to an EMS call in 62% of cases, and a subsequent resuscitation effort in 67% of the cases, the researchers estimated that appropriate shocks prevented 81 cases of presumed cardiac arrest.

That corresponds with about 33% of the observed decline in out-of-hospital cardiac arrest incidence during the study periods, they wrote.

Further sensitivity analyses determined that between 16% and 63% of the reduction can be attributed to ICD implantation.

Koster and colleagues noted that the decline in ventricular fibrillation as the presenting arrhythmia in cardiac arrest was accompanied by a significant increase in nonventricular-fibrillation arrest -- one that is far larger than the drop in ventricular-fibrillation-related arrest.

This indicates that more patients suffered a cardiac arrest out of hospital, but the reasons for this increase are unclear, they wrote.

The study was limited because the researchers relied on a number of assumptions to estimate the contribution of multiple successful shock episodes, the probability of an EMS call after collapse, and the probability of a resuscitation effort after EMS arrival.

They also noted that other factors "must play at least an equal role in the explanation for the observed decline in ventricular fibrillation-related out-of-hospital cardiac arrest."

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